Piezoelectric element, liquid-ejecting head, and liquid-ejecting apparatus

ABSTRACT

A piezoelectric element includes a piezoelectric layer and electrodes provided to the piezoelectric layer. The piezoelectric layer consists of a complex oxide containing bismuth, cerium, iron and cobalt and the molar ratio of cobalt to the total of iron and cobalt is 0.125 or more and 0.875 or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2010-107740 filed May 7, 2010, the contents of which arehereby incorporated by reference in their entirety.

BACKGROUND

1. Technical Field

The present invention relates to a liquid ejecting head including apiezoelectric element that causes a change in pressure in apressure-generating chamber communicating with a nozzle opening and hasa piezoelectric layer and electrodes for applying a pressure to thepiezoelectric layer, and relates to a liquid ejecting apparatus and apiezoelectric element.

2. Related Art

In some of piezoelectric actuators used in liquid ejecting heads, apiezoelectric element having a structure in which a piezoelectric layermade of a piezoelectric material, for example, a crystallized dielectricmaterial, exhibiting an electromechanical conversion function isdisposed between two electrodes is used. A typical example of the liquidejecting head is an ink jet recording head in which a diaphragmconfigures a part of a pressure-generating chamber communicating with anozzle opening for discharging ink droplets and a pressure is applied tothe ink in the pressure-generating chamber by deforming the diaphragm bya piezoelectric element to discharge the ink as droplets from the nozzleopening.

The piezoelectric material used as the piezoelectric layer(piezoelectric ceramic) configuring such a piezoelectric element isrequired to have a high piezoelectric property, and typical examples ofsuch piezoelectric material include lead zirconate titanate (PZT) (seeJP-A-2001-223404).

However, from the viewpoint of an environmental problem, there is ademand for a piezoelectric material having a less content of lead. As anexample of the piezoelectric material not containing lead, BiFeO₃ havinga perovskite structure shown by ABO₃ is known, but the BiFeO₃ systempiezoelectric material has low insulation and, therefore, has a problemof easily causing a leakage current. Accordingly, there is a problemthat it is difficult to apply the material to liquid ejecting heads. Inaddition, the amount of deflection is small, compared to that of PZT.Accordingly, there is a demand for a piezoelectric material giving alarge amount of deflection and having an excellent piezoelectricproperty.

These problems are not only of ink jet recording heads, of cause, butalso of other liquid ejecting heads for discharging droplets other thanink. In addition, these problems are of piezoelectric elements that areused for devices other than liquid ejecting heads.

SUMMARY

An advantage of some aspects of the invention is to provide a liquidejecting head, a liquid ejecting apparatus, and a piezoelectric elementthat are reduced in environmental loads, leakage currents in which areprevented, and have excellent piezoelectric properties.

An aspect of the invention for solving the above-mentioned problems is aliquid ejecting head including a pressure-generating chambercommunicating with a nozzle opening and a piezoelectric element having apiezoelectric layer and electrodes provided to the piezoelectric layer,wherein the piezoelectric layer is configured of a complex oxide havinga perovskite structure containing bismuth, cerium, iron, and cobalt sothat the molar ratio of cobalt to the total of iron and cobalt is 0.125or more and 0.875 or less.

In this aspect, a leakage current is prevented, and an excellentpiezoelectric property is provided. In addition, since lead is notcontained, environmental loads can be reduced.

In a preferred aspect of the invention, the bismuth and the cerium arecontained in the A site, and the iron and cobalt are contained in the Bsite.

In another preferred aspect of the invention, the complex oxide isrepresented by the following general formula:(Bi_(1-x),Ce_(3x/4))(Co_(1-δ),Fe_(δ))O₃  (1)

The piezoelectric layer preferably has a monoclinic crystallinestructure. By doing so, a more excellent piezoelectric property can beobtained.

The complex oxide may further contain lanthanum. The complex oxidepreferably contains lanthanum at a molar ratio of 0.05 or more and 0.20or less with respect to the total of bismuth, cerium, and lanthanum.

Another aspect of the invention is a liquid ejecting apparatus includingthe above-described liquid ejecting head according to an aspect of theinvention.

In this aspect, a liquid ejecting apparatus, the leakage current inwhich is prevented and the piezoelectric property of which is excellent,can be realized. In addition, since lead is not contained, environmentalloads can be reduced.

Another aspect of the invention is a piezoelectric element including apiezoelectric layer and electrodes provided to the piezoelectric layer,wherein the piezoelectric layer is configured of a complex oxide havinga perovskite structure containing bismuth, cerium, iron, and cobalt sothat the molar ratio of cobalt to the total of iron and cobalt is 0.125or more and 0.875 or less.

In this aspect, a piezoelectric element, the leakage current in which isprevented and the piezoelectric property of which is excellent, can berealized. In addition, since lead is not contained, environmental loadscan be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is an exploded perspective view of schematically illustrating theconstitution of a recording head according to Embodiment 1.

FIG. 2 is a plan view of the recording head according to Embodiment 1.

FIG. 3 is a cross-sectional view of the recording head according toEmbodiment 1.

FIG. 4 is a diagram showing the density of states of BiFeO₃ in a perfectcrystalline state.

FIG. 5 is a diagram showing the density of states when 12.5% of Bi inBiFeO₃ was lost.

FIG. 6 is a diagram showing the density of states when 12.5% of Bi inBiFeO₃ was replaced by Ce.

FIG. 7 is a schematic diagram of a complex oxide crystal having aperovskite structure.

FIG. 8A is a cross-sectional view of a recording head in its productionprocess according to Embodiment 1.

FIG. 8B is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 9A is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 9B is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 9C is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 10A is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 10B is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 11A is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 11B is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 11C is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 12A is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 12B is a cross-sectional view of the recording head in itsproduction process according to Embodiment 1.

FIG. 13 is a view schematically showing the constitution of a recodingapparatus according to an embodiment of an aspect of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Embodiment 1

FIG. 1 is an exploded perspective view of schematically illustrating theconstitution of an ink jet recording head which is an example of theliquid ejecting head according to Embodiment 1 of the invention. FIG. 2is a plan view of the recording head shown in FIG. 1, and FIG. 3 is across-sectional view taken along the line III-III of FIG. 2. As shown inFIGS. 1 to 3, the passage-forming substrate 10 of this embodiment is asingle-crystal silicon substrate, and an elastic film 50 of silicondioxide is disposed on one surface thereof.

The passage-forming substrate 10 is provided with a plurality ofpressure-generating chambers 12 arranged in parallel in their widthdirection. Furthermore, the passage-forming substrate 10 is providedwith a communicating portion 13 in an area on an outer side in thelongitudinal direction of the pressure-generating chambers 12, and thecommunicating portion 13 and each pressure-generating chamber 12 arecommunicated with each other through an ink-supplying path 14 and acommunicating path 15 provided to each of the pressure-generatingchambers 12. The communicating portion 13 communicates with a manifoldportion 31 of a protective substrate described below to constitute apart of the manifold serving as the ink chamber common to all thepressure-generating chambers 12. The ink-supplying path 14 has a widthnarrower than that of the pressure-generating chamber 12 and maintains aconstant flow resistance of the ink flowing in the pressure-generatingchamber 12 from the communicating portion 13. Incidentally, in theembodiment, the ink-supplying path 14 is formed by narrowing the widthof the flow path from one side, but it may be formed by narrowing thewidth of the flow path from both sides. Alternatively, the ink-supplyingpath may be formed by narrowing the flow path from the thicknessdirection, instead of narrowing the width of the flow path. Therefore,in this embodiment, the passage-forming substrate 10 is provided with aliquid passage composed of the pressure-generating chamber 12, thecommunicating portion 13, the ink-supplying path 14, and thecommunicating path 15.

In addition, the passage-forming substrate 10 is bonded to a nozzleplate 20 with, for example, an adhesive or a thermal adhesive film onthe opened surface side. The nozzle plate 20 is perforated with nozzleopenings 21 that communicate with the corresponding pressure-generatingchambers 12 in the vicinity of the ends of the pressure-generatingchambers 12 on the side opposite to the ink-supplying path 14. Thenozzle plate 20 is made of, for example, a glass ceramic, asingle-crystal silicon substrate, or stainless steel.

Furthermore, as described above, the elastic film 50 is disposed on theother side of the passage-forming substrate 10 than the opened surfaceside. On the elastic film 50, an adhesive layer 56 made of, for example,titanium oxide is disposed to increase the adhesion of a first electrode60 to a base such as the elastic film 50. Furthermore, an insulatingfilm made of, for example, zirconium oxide, may be disposed between theelastic film 50 and the adhesive layer 56 as necessary.

On the adhesive layer 56, the first electrode 60, a piezoelectric layer70 that is a thin film having a thickness of 2 μm or less, preferably0.3 to 1.5 μm, and a second electrode 80 are laminated to constitute apiezoelectric element 300. Herein, the piezoelectric element 300 is aportion including the first electrode 60, the piezoelectric layer 70,and the second electrode 80. In general, one of the electrodes of thepiezoelectric element 300 is formed as a common electrode, and the otherelectrode and the piezoelectric layer 70 are formed by patterning foreach pressure-generating chamber 12. In the embodiment, the firstelectrode 60 is formed as the common electrode of the piezoelectricelements 300, and the second electrode 80 is the individual electrode ofeach piezoelectric element 300, but these may be reversed depending on adriving circuit or wiring. Furthermore, herein, the piezoelectricelement 300 and a diaphragm, which is deformed by driving thepiezoelectric element 300, are collectively referred to as an actuator.In the above-mentioned example, the elastic film 50, the adhesive layer56, the first electrode 60, and the insulating film disposed accordingto need function as the diaphragm, but the diaphragm is not limitedthereto. For example, the elastic film 50 and the adhesive layer 56 maynot be provided. Alternatively, the piezoelectric element 300 itself maysubstantially function as a diaphragm.

In the embodiment, the piezoelectric layer 70 is made of a complex oxidehaving a perovskite structure containing bismuth (Bi), cerium (Ce), iron(Fe), and cobalt (Co), wherein the molar ratio of cobalt to the total ofiron and cobalt is 0.125 or more and 0.875 or less. By doing so, asdescribed below, a leakage current is prevented, and the piezoelectricproperty is improved. In addition, since lead is not contained, theenvironmental loads can be reduced. Examples of the complex oxideaccording to the embodiment include those containing bismuth and ceriumin the A site of the perovskite structure and iron and cobalt in the Bsite.

Bismuth contained in, for example, BiFeO₃ tends to volatilize during theproduction process, in particular, during the calcination of thepiezoelectric layer, which has a problem that crystal deficiency of theA site tends to occur. If Bi falls out, at the exact time oxygen is lostfor maintaining a balance in the number of electrons. This oxygendefect's presence itself narrows the band gap of the piezoelectricelement, which is a direct cause of generating a leakage current. Theoxygen defect can be avoided by avoiding Bi defect. As a method forthat, it is suggested to add Bi in advance in an amount that isexcessive than that of the stoichiometric composition. However,excessive Bi enters not only the A site but also the B site at a certainratio. The Bi entered the B site serves as an electron supplier, whichcauses a problem of causing leakage current in the piezoelectricelement.

In this embodiment, by containing bismuth and cerium in the A site, evenif deficiency has occurred on the position of bismuth, cerium enters theA site to maintain the insulation. That is, a decrease in insulation dueto deficiency of bismuth is prevented to make the piezoelectric layer 70have a high insulating property. By doing so, a leakage current in thepiezoelectric element 300 can be prevented. For example, the leakagecurrent of the piezoelectric layer 70 when a voltage of 25 V is appliedcan be kept to be 1.0×10⁻¹ A/cm² or less, preferably 1.0×10⁻³ A/cm² orless. Note that a voltage of 25 V is a typical drive voltage that isapplied to each piezoelectric element of ink jet recording heads.

It will be described below that the piezoelectric layer 70 has anexcellent insulating property, using bismuth ferrate (BiFeO₃) as anexample with reference to FIGS. 4 to 6. Note that the followingexplanation will describe an insulating property by focusing on the Asite of a complex oxide.

FIGS. 4 to 6 are diagrams showing the density of states of each crystaldetermined by using first principle electronic state calculation. Thehorizontal axis shows the energy difference (eV) of electrons, and thevertical axis shows the density of states (DOS) of electrons. The plusside of the density of states (higher than 0/eV) shows the up-spin, andthe minus side shows the down-spin. As the conditions for the firstprinciple electronic state calculation, an ultra-soft pseudopotentialbased on a density functional method within the range of generalizedgradient approximation (GGA) was used. For the transition metal atoms inthe B site, in order to take in the strong correlation effect due tod-electron orbital localization, a GGA plus U method (GGA+U method) wasused. The cut-off of the wave function and the cut-off of the chargedensity are respectively 20 hartree and 360 hartree. The super cell ofthe crystal used for the calculation is composed of 2×2×2 (=8) ABO₃-typeperovskite structures. The mesh of the reciprocal lattice point (kpoint) is (4×4×4). Furthermore, the position of each atom is optimizedso that the force acting on the atoms is minimized. FIG. 4 is a diagramshowing the density of states of bismuth ferrate (BiFeO₃) in a perfectcrystalline state, FIG. 5 is a diagram showing the density of stateswhen 12.5% of Bi in bismuth ferrate (BiFeO₃) was lost, and FIG. 6 is adiagram showing the density of states when 12.5% of Bi in bismuthferrate (BiFeO₃) was replaced by Ce.

The antiferromagnetic states of all systems in the cases shown in FIGS.4 to 6 were stable.

As shown in FIG. 4, when BiFeO₃ is a complete crystal, that is, whenthere are no holes in both sites and no replacement of Bi by anotherelement, the Fermi level is the top of the valence band to provide aninsulating property. Incidentally, the Fermi level is defined as thehighest energy level occupied by an electron in one-electron energyobtained by electronic-state simulation.

As shown in FIG. 5, it was confirmed that in BiFeO₃, when deficiency isgenerated by causing loss of a part of bismuth (Bi), peaks project tothe plus side than the energy of 0 eV, that is, the Fermi level iswithin the range of a valence band to lose the insulating property andgenerate holes to give a p-type. It was confirmed that the area ofdensity of states of the valence band holes (the projection area ofpeaks in the plus side) obtained by integration is comparable to threeelectrons. This revealed that bismuth in the crystal system of BiFeO₃contributes as 3+.

Furthermore, as shown in FIG. 6, it was confirmed that when a part ofbismuth (Bi) of BiFeO₃ is forcedly replaced by cerium, peaks project tothe minus side than the energy of 0 eV, that is, the Fermi level iswithin the range of a conduction band to lose the insulating property togive an n-type. It was confirmed that the area of density of states ofthe conduction electrons (the projection area of peaks in the minusside) obtained by integration is comparable to one electron. It wasconfirmed from FIGS. 4 to 6 that cerium contribute as 4+ and functionsas an n-type donor.

From the above, it was confirmed that a high insulating property can bemaintained by containing bismuth and cerium in the A site, that is, byreplacing a part of bismuth by cerium. More specifically, it wasconfirmed that charge compensation for crystal deficiency of bismuth isperformed by cerium to maintain the insulating property. Furthermore, inthe above-described example, the insulating property has been describedby using BiFeO₃ and focusing on the A site, but the behavior, such asthe position of Fermi level, is the same in the case that the B sitecontains cobalt, as described below.

Herein, when the deficiency amount of bismuth is represented by x andthe addition amount of cerium is represented by y, the A site can beexpressed by Bi_(1-x)Ce_(y). As proved based on the above-describedfirst principle calculation, bismuth functions as trivalent, and ceriumfunctions as tetravalent. The charge neutrality of the crystal can bemaintained by keeping the A site trivalent in total. Therefore, thecomposition balance of Bi and Ce may satisfy 3(1-x)+4y=3. That is, whenthe deficiency amount of Bi is x, cerium may be contained in an amountof 3x/4. Therefore, for example, a complex oxide satisfying (Bi_(1-x),Ce_(3x/4)) (Co_(1-δ), Fe_(δ))O₃ can be obtained by adding Ce in anamount of 3x/4 for the estimated deficiency amount x of Bi during theproduction process. Under such conditions, even if the number ofelectrons is decreased by deficiency of Bi, the excessive electronspossessed by added cerium compensate for the decrease to hardly causeoxygen defect. Experimentally, the molar ratio of cerium in the complexoxide to the total of bismuth and cerium is preferably 0.01 or more and0.13 or less. By doing so, the system can have a higher insulatingproperty and less leakage current compared to a system not containing Cesuch as a BiFeO₃ system complex system.

The complex oxide may contain lanthanum in the A site. Appearance of ahetero phase other than the perovskite structure is prevented bycontaining lanthanum. Since lanthanum is a metal having an ionic valenceof 3+, the presence of this metallic element in the A site does notchange the “valence balance” of the invention and does not adverselyaffect the leakage current conditions. The molar ratio of lanthanumcontained in the A site is 0.05 or more and 0.20 or less with respect tothe total of bismuth, cerium, and lanthanum.

The complex oxide contains bismuth (Bi) in the A site and iron (Fe) andcobalt (Co) in the B site in a molar ratio of cobalt to the total ofiron and cobalt of 0.125 or more and 0.875 or less. Thus, in theembodiment, the complex oxide constituting the piezoelectric layer 70contains iron and cobalt, which have different atomic radii from eachother, in the B site position at a certain ratio, and, thereby, theinsulating property and the magnetic property can be maintained. Inaddition, since such a complex oxide has a morphotropic phase boundary(MPB), the piezoelectric layer 70 can have an excellent piezoelectricproperty. In particular, when the molar ratio of cobalt to the total ofiron and cobalt is approximately 0.5, for example, the piezoelectricconstant is increased to provide a particularly excellent piezoelectricproperty.

FIG. 7 is a schematic diagram of a complex oxide crystal having aperovskite structure. Iron and cobalt contained in the B site of thecomplex oxide according to the embodiment have magnetic properties. Asshown in FIG. 7, in the complex oxide having a perovskite structure ofthe embodiment, the antiferromagnetic structure is maintained by amagnetic network of iron or cobalt, which is a metal in the B site, andoxygen.

Furthermore, the piezoelectric layer 70 of the embodiment has amonoclinic crystalline structure. That is, the piezoelectric layer 70made of a complex oxide having a perovskite structure has monoclinicsymmetry. Such a piezoelectric layer 70 can obtain a high piezoelectricproperty. The reason thereof is thought that, in such a structure, thepolarization moment of the piezoelectric layer easily rotates by anelectric field applied in the direction perpendicular to a plane. In thepiezoelectric layer, the amount of a change in the polarization momentand the amount of a change in the crystal structure are directly linkedto each other to exactly provide a piezoelectric property. From theabove, in a structure in which a change in the polarization moment tendsto occur, a high piezoelectric property can be obtained.

The piezoelectric layer 70 is preferably in an engineered domainarrangement in which the polarization direction is tilted at a certainangle (50 to 60 degrees) with respect to the vertical direction of thefilm plane (the thickness direction of the piezoelectric layer 70).

Each second electrode 80, which is the individual electrode of thepiezoelectric element 300, is connected to a lead electrode 90 made of,for example, gold (Au) that is drawn out from the vicinity of the end onthe ink-supplying path 14 side and extends on the elastic layer 56.

Above the passage-forming substrate 10 provided with such piezoelectricelements 300, that is, above the first electrode 60, the adhesive layer56, and the lead electrodes 90, a protective substrate 30 having themanifold portion 31 constituting at least a part of a manifold 100 isbonded with an adhesive 35. In the embodiment, the manifold portion 31is formed along the width direction of the pressure-generating chambers12 so as to pass through the protective substrate 30 in the thicknessdirection and communicates with the communicating portion 13 of thepassage-forming substrate 10 to constitute the manifold 100 serving as acommon ink chamber for the pressure-generating chambers 12.Alternatively, the communicating portion 13 of the passage-formingsubstrate 10 may be divided so as to correspond to eachpressure-generating chamber 12, and only the manifold portion 31 mayserve as the manifold. Furthermore, for example, the passage-formingsubstrate 10 may be provided with only the pressure-generating chambers12, and members (for example, the elastic film 50 and the adhesive layer56) interposed between the passage-forming substrate 10 and theprotective substrate 30 may be provided with the ink-supplying paths 14communicating with the manifold 100 and the correspondingpressure-generating chambers 12.

The protective substrate 30 is provided with a piezoelectric elementholding portion 32, at the area facing the piezoelectric elements 300,having a space that is enough not to hinder the movement of thepiezoelectric elements 300. The space of the piezoelectric elementholding portion 32 may be sealed or not be sealed as long as it isenough not to hinder the movement of the piezoelectric elements 300.

The protective substrate 30 is preferably made of a material havingalmost the same coefficient of thermal expansion as that of thepassage-forming substrate 10, for example, made of a glass or ceramicmaterial. In this embodiment, the protective substrate 30 is asingle-crystal silicon substrate, which is the same material as that ofthe passage-forming substrate 10.

The protective substrate 30 is provided with a through-hole 33 passingthrough the protective substrate 30 in the thickness direction. Thethrough-hole 33 is formed so that the vicinity of the end of the leadelectrode 90 drawn out from each piezoelectric element 300 is exposed inthe through-hole 33.

Furthermore, a driving circuit 120 for driving the piezoelectricelements 300 arranged parallel is fixed on the protective substrate 30.The driving circuit 120 may be, for example, a circuit board or asemiconductor integrated circuit (IC). The driving circuit 120 and thelead electrodes 90 are electrically connected to each other throughconnecting wire 121 made of conductive wire such as bonding wire.

In addition, a compliance substrate 40 composed of a sealing film 41 anda fixing plate 42 is bonded on the protective substrate 30. Herein, thesealing film 41 is formed of a flexible material having a low rigidityand seals one side of the manifold portion 31. The fixing plate 42 isformed of a relatively hard material. The fixing plate 42 is providedwith an opening 43 by completely removing the fixing plate 42 at thearea facing the manifold 100 in the thickness direction. Therefore, theone side of the manifold 100 is sealed with only the sealing film 41having flexibility.

In such an ink jet recoding head I of the embodiment, ink is fed throughan ink inlet connected to exterior ink supplying means (not shown) tofill the inside from the manifold 100 to the nozzle openings 21 withink. Then, a voltage is applied between the first electrode 60 and thesecond electrode 80 corresponding to each pressure-generating chamber 12according to a recording signal from the driving circuit 120 toflexurally deform the elastic film 50, the adhesive layer 56, the firstelectrode 60, and the piezoelectric layer 70. Thereby, the pressure ineach pressure-generating chamber 12 is increased, and ink droplets aredischarged from the nozzle opening 21.

Then, an example of the process of producing the piezoelectric elementof the ink jet recoding head of the embodiment will be described withreference to FIGS. 8A, 8B, 9A to 9C, 10A, 10B, 11A to 11C, 12A, and 12B.

First, as shown in FIG. 8A, a silicon dioxide film of, for example,silicon dioxide (SiO₂), constituting the elastic film 50 is formed onthe surface of a silicon wafer as the passage-forming substrate wafer110 by, for example, thermal oxidization. Then, as shown in FIG. 8B, anadhesive layer 56 of, for example, titanium oxide is formed on theelastic film 50 (silicon dioxide film) by, for example, reactivesputtering or thermal oxidation.

Then, as shown in FIG. 9A, a first electrode 60 is formed on theadhesive layer 56. Specifically, a first electrode 60 made of platinum,iridium, iridium oxide, or a layered structure thereof is formed on theadhesive layer 56. The adhesive layer 56 and the first electrode 60 canbe formed by, for example, sputtering or vapor deposition.

Then, a piezoelectric layer 70 is laminated on the first electrode 60.The process of producing the piezoelectric layer 70 is not particularlylimited, but, for example, the piezoelectric layer 70 can be formed by ametal-organic decomposition (MOD) method, in which a piezoelectric layer70 of a metal oxide is produced by dissolving/dispersing anorganometallic compound in a solvent and applying and drying thesolution and firing it at high temperature, or by chemical solutiondeposition such as a sol-gel method. The piezoelectric layer 70 may beformed by another method, such as a laser ablation method, a sputteringmethod, a pulse laser deposition method (PLD method), a CVD method, oran aerosol deposition method.

In a specific example of the procedure for forming the piezoelectriclayer 70, first, as shown in FIG. 9B, on the first electrode 60, a solor an MOD solution (precursor solution) containing organometalliccompounds, specifically, organometallic compounds containing Bi, Ce, Fe,Co, and, as necessary, La at a ratio so as to give a target compositionratio is applied by, for example, spin coating to form a piezoelectricprecursor film 71 (application step).

The precursor solution to be applied is prepared by mixingorganometallic compounds that can form a complex oxide containing Bi,Ce, Fe, and Co at desired molar ratios and dissolving or dispersing themixture in an organic solvent such as alcohol. On this occasion, theaddition amount of cerium is adjusted to an amount of 3x/4 for theestimated deficiency amount x of Bi.

Herein, the phrase “organometallic compounds that can form a complexoxide containing Bi, Ce, Fe, and Co” refers to a mixture oforganometallic compounds each containing at least one metal selectedfrom Bi, Ce, Fe, and Co. The organometallic compound may contain La. Asthe organometallic compounds respectively containing Bi, Ce, Fe, Co, andLa, for example, metal alkoxides, organic acid salts, and β-diketonecomplexes can be used. Examples of the organometallic compoundcontaining Bi include bismuth 2-ethylhexanoate. Examples of theorganometallic compound containing Fe include iron 2-ethylhexanoate.Examples of the organometallic compound containing Ce include cerium2-ethylhexanoate. Examples of the organometallic compound containing Coinclude cobalt 2-ethylhexanoate. Examples of the organometallic compoundcontaining La include lanthanum 2-ethylhexanoate. An organometalliccompound containing two or more of Bi, Ce, Fe, Co, and La may be used.

Then, the piezoelectric precursor film 71 is heated at a predeterminedtemperature for a predetermined time for drying (drying step).Subsequently, the dried piezoelectric precursor film 71 is heated to apredetermined temperature and is kept at the temperature for apredetermined period of time for degreasing (degreasing step). Herein,the term “degreasing” means that organic components contained in thepiezoelectric precursor film 71 are eliminated as, for example, NO₂,CO₂, or H₂O. The atmospheres for the drying step and the degreasing stepare not limited, and these steps may be performed in the air or in aninert gas.

Then, as shown in FIG. 9C, the piezoelectric precursor film 71 is heatedto a predetermined temperature, for example, about 600 to 800° C., andis kept at the temperature for a predetermined period of time forcrystallization to form a piezoelectric film 72 (firing step). Theatmosphere for the firing step is also not limited, and the step may beperformed in the air or in an inert gas.

As the heating apparatus used in the drying step, the degreasing step,or the firing step, for example, a rapid thermal annealing (RTA)apparatus performing heating by irradiation with an infrared lamp or ahot plate can be used.

Then, as shown in FIG. 10A, the first electrode 60 and the first layerof the piezoelectric film 72 are simultaneously patterned so as to havean incline at their side faces using a resist (not shown) having apredetermined shape as a mask on the piezoelectric film 72.

Then, after removal of the resist, a piezoelectric layer 70 composed ofa plurality of the piezoelectric films 72, as shown in FIG. 10B, andhaving a predetermined thickness is formed by repeating more than oncethe application step, the drying step, and the degreasing step, or theapplication step, the drying step, the degreasing step, and the firingstep, according to a desired thickness, etc. For example, when thethickness of each application of a solution is about 0.1 μm, the totalthickness of the piezoelectric layer 70 composed of, for example, tenlayers of the piezoelectric films 72 is about 1.1 μm. In thisembodiment, the piezoelectric layer 70 is a laminated layer of thepiezoelectric films 72, but may be a single layer.

After thus forming the piezoelectric layer 70, as shown in FIG. 11A, asecond electrode 80 of, for example, platinum is formed on thepiezoelectric layer 70 by sputtering. Subsequently, the piezoelectriclayer 70 and the second electrode 80 are simultaneously patterned in thearea corresponding to the pressure-generating chambers 12 to formpiezoelectric elements 300 each composed of the first electrode 60, thepiezoelectric layer 70, and the second electrode 80. The patterning ofthe piezoelectric layer 70 and the second electrode 80 can be performedat once by dry etching through a resist (not shown) having apredetermined shape. Then, according to necessary, post annealing may beperformed in a temperature range of 600 to 800° C. By doing so, theinterface between the piezoelectric layer 70 and the first electrode 60or the second electrode 80 can be improved, and also the crystallinityof the piezoelectric layer 70 can be improved.

Then, as shown in FIG. 11B, a lead electrode 90 of, for example, gold(Au) is formed on the entire surface of the passage-forming substratewafer 110 and then is patterned through a mask pattern (not shown) of aresist or the like to form the lead electrodes 90 corresponding to therespective piezoelectric elements 300.

Then, as shown in FIG. 11C, a protective substrate wafer 130 that is asilicon wafer for forming a plurality of protective substrates 30 isbonded to the passage-forming substrate wafer 110 on the piezoelectricelements 300 side with an adhesive 35, and, subsequently, thepassage-forming substrate wafer 110 is thinned to a predeterminedthickness.

Subsequently, as shown in FIG. 12A, a new mask film 52 is formed on thepassage-forming substrate wafer 110 and patterned into a predeterminedshape.

Then, as shown in FIG. 12B, the passage-forming substrate wafer 110 isanisotropically etched (wet-etched) using an alkaline solution, such asKOH, through the mask film 52 to form the pressure-generating chambers12, the communicating portion 13, the ink-supplying paths 14, and thecommunicating paths 15 corresponding to the piezoelectric elements 300.

Then, unneeded portions at the outer peripheral portions of thepassage-forming substrate wafer 110 and the protective substrate wafer130 are removed by cutting, e.g., by dicing. The mask film 52 on theopposite side of the passage-forming substrate wafer 110 from theprotective substrate wafer 130 is removed. Subsequently, a nozzle plate20 perforated with nozzle openings 21 is bonded to the passage-formingsubstrate wafer 110, and a compliance substrate 40 is bonded to theprotective substrate wafer 130, and the passage-forming substrate wafer110 and other associated components are divided into individualchip-sized passage-forming substrates 10 and other components as shownin FIG. 1 to give the ink jet recording head I of the embodiment.

Other Embodiment

An embodiment according to an aspect of the invention has been describedabove, but the basic constitution of the invention is not limitedthereto. For example, in the above-described embodiment, asingle-crystal silicon substrate is used as the passage-formingsubstrate 10, but the passage-forming substrate 10 is not limitedthereto and may be, for example, a SOI substrate or a glass substrate.

In addition, in the above-described embodiment, as an example, thepiezoelectric elements 300 are formed by sequentially laminating a firstelectrode 60, a piezoelectric layer 70, and a second electrode 80 on asubstrate (passage-forming substrate 10), but is not particularlylimited thereto. The invention can be applied to, for example, alongitudinal vibration-type piezoelectric element that extends andcontracts in the axial direction by alternately laminating apiezoelectric material and an electrode-forming material.

The ink jet recording head of the embodiment constitutes a part of arecording head unit including an ink flow path that communicates with,for example, an ink cartridge and is mounted on an ink jet recordingapparatus. FIG. 13 is a schematic view showing an example of the ink jetrecording apparatus.

As shown in FIG. 13, the recording head units 1A and 1B including theink jet recording heads I are detachably provided with cartridges 2A and2B constituting ink supplying means. A carriage 3 on which the recordinghead units 1A and 1B are mounted is set to a carriage axis 5, which isfixed to an apparatus body 4, in a manner that the carriage 3 is movablein the axial direction. The recording head units 1A and 1B discharge,for example, a black ink composition and a color ink composition,respectively.

Driving force of a driving motor 6 is transferred to the carriage 3through a plurality of gears (not shown) and a timing belt 7, andthereby the carriage 3, on which the recording head units 1A and 1B aremounted, is moved along the carriage axis 5. The apparatus body 4 isprovided with a platen 8 along the carriage axis 5, and a recordingsheet S, serving as a recording medium such as paper, is fed by, forexample, a feeding roller (not shown) and is wrapped around the platen 8and thereby transported.

In the example shown in FIG. 13, the ink jet recording head units 1A and1B each have one ink jet recording head I, but are not particularlylimited thereto. For example, one ink jet recording head unit 1A or 1Bmay have two or more ink jet recording heads.

In the above-described embodiment, an ink jet recording head has beendescribed as an example of the liquid ejecting head, but the inventionbroadly covers general liquid ejecting heads and can be applied toliquid ejecting heads that eject liquid other than ink. Examples of theother liquid ejecting heads include various types of recording headsused in image recording apparatuses such as printers, coloring materialejecting heads used for producing color filters of, for example, liquidcrystal displays, electrode material ejecting heads used for formingelectrodes of, for example, organic EL displays or field emissiondisplays (FEDs), and bio-organic material ejecting heads used forproducing bio-chips.

Since the piezoelectric element of the invention shows a good insulatingproperty and a good piezoelectric property, as described above, it canbe applied to piezoelectric elements of liquid ejecting headsrepresented by ink jet recording heads, but the application is notlimited thereto. For example, the piezoelectric element can be appliedto piezoelectric elements of, for example, ultrasonic devices such asultrasonic transmitters, ultrasonic motors, piezoelectric transformers,and various types of sensors such as infrared sensors, ultrasonicsensors, thermal sensors, pressure sensors, and pyroelectric sensors. Inaddition, the invention can be similarly applied to ferroelectricdevices such as ferroelectric memories.

1. A piezoelectric element comprising: a piezoelectric layer andelectrodes provided to the piezoelectric layer, wherein thepiezoelectric layer consists of a complex oxide containing bismuth,cerium, iron, and cobalt and the molar ratio of cobalt to the total ofiron and cobalt is 0.125 or more and 0.875 or less.
 2. The piezoelectricelement according to claim 1, wherein the bismuth and the cerium arecontained in the A site and the iron and the cobalt are contained in theB site.
 3. The piezoelectric element according to claim 1, wherein thecomplex oxide is represented by the following formula:(Bi_(1-x),Ce_(3x/4))(Co_(1-δ),Fe_(δ))O₃  (1).
 4. The piezoelectricelement according to claim 1, wherein the piezoelectric layer has amonoclinic crystalline structure.
 5. The piezoelectric element accordingto claim 1, wherein the complex oxide further contains lanthanum.
 6. Thepiezoelectric element according to claim 5, wherein the complex oxidecontains lanthanum at a molar ratio of 0.05 or more and 0.20 or lesswith respect to the total of bismuth, cerium, and lanthanum.
 7. A liquidejecting head comprising the piezoelectric element according to claim 1.8. A liquid ejecting apparatus comprising the liquid ejecting headaccording to claim 7.